The present invention relates to a hybrid magnet type DC motor having a stator that includes a coil and a permanent magnet.
A small motor, which consumes little electricity and brings high level torque, has widely been used in the field of, for example, automobile, office automation hardware, vending machine and medical and welfare equipment. Most of the motors used in these fields are normally comprised of a permanent magnet. This kind of motor has been grown technically and it is difficult to achieve high efficiency, reduction in size and weight and high level torque. Then, a hybrid magnet type DC motor 50 shown in FIG. 6 has been proposed.
As shown in FIG. 6, the DC motor 50 has a cylindrical yoke 55 and an armature 51 that is accommodated in the yoke 55. The armature 51 has a rotation core 53 that is fitted around a rotation shaft 52 and a plurality of rotation coils 54 that are wound around the rotation core 53. The rotation core 53 has a plurality of tees 53a that radiate in all direction. A stator 56 is fixed to the inner surface of the yoke 55. The stator 56 includes a pair of electromagnets 57, 58 and a pair of permanent magnets 59, 60 and constitutes a hybrid magnet. A prescribed gap is provided between the stator 56 and the outer surface of the armature 51. The gap is so small that it is not visibly illustrated in FIG. 6.
The electromagnets 57, 58 have fixed cores 61, 62 and fixed coils 63, 64 that are wound around portions of the fixed cores 61, 62. The fixed cores 61, 62 have at one end pole cores 65, 66 that are made by semi-cylindrical plates. The fixed coils 63, 64 are wound around portions of the fixed cores 61, 62 (the portions shown by broken lines) that radially project from the pole cores 65, 66. The pole cores 65, 66 face to the tees 53a of the armature 51 with the prescribed gap in between. The pole cores 65, 66 have extending portions 65a, 66a that extend in the circumferential direction of the stator 56 beyond both ends of the corresponding fixed coils 63, 64. The outer surfaces of the extending portions 65a, 66a contact the inner surfaces of the permanent magnets 59, 60.
The permanent magnet 59 has two magnet pieces: a first magnet piece 59a and a second magnet piece 59b, while the permanent magnet 60 has two magnet pieces: a first magnet piece 60a and a second magnet piece 60b. The magnet pieces 59a, 59b, 60a, 60b have a sectorial cross-sectional shape. The magnet pieces 59a and 59b of the permanent magnet 59 are arranged such that the magnetic direction of the first magnet piece 59a is opposite to that of the second magnet piece 59b. The magnet pieces 60a and 60b of the permanent magnet 60 are arranged such that the magnetic direction of the magnet piece first 60a is opposite to that of the second magnet piece 60b. Specifically, the first magnet pieces 59a, 60a of the permanent magnets 59, 60 are magnetized to be an N-pole at their inner surfaces and an S-pole at their outer surfaces. The second magnet pieces 59b, 60b of the permanent magnets 59, 60 are magnetized to be an S-pole at their inner surfaces and an N-pole at their outer surfaces. A resin piece T, which functions as a magnetic insulator T, is provided between the first and second magnet pieces 59a, 59b. Similarly, the resin piece T is provided between the first and second magnet pieces 60a, 60b. 
Core plates 67 contact the outer surfaces of the permanent magnets 59, 60. The magnetism of the first and second magnet pieces 59a, 59b, 60a, 60b passes through the corresponding core plates 67. The insulators 68, which are made of resin, are located between the core plates 67 and the fixed yoke 55. The insulators 68 magnetically insulate the corresponding permanent magnets 59, 60 from the fixed yoke 55. Accordingly, magnetic flux, which is produced in the permanent magnets 59, 60, passes through the pole cores 65, 66.
In the above DC motor 50, the contacting area of the pole cores 65, 66 and the permanent magnets 59, 60 can be increased, which increases torque of the motor 50, without increasing the diameter of the yoke 55.
In the above DC motor 50, however, the magnetic flux produced between the magnet pieces 59a, 59b of the permanent magnet 59 and the magnet pieces 60a, 60b of the permanent magnet 60 flows through the corresponding core plates 67. The insulators 68 are located to prevent the magnet flux from leaking to the yoke 55. When the magnetism of the permanent magnets 59, 60 is increased, however, the magnetic flux produced in the permanent magnets 59, 60 leaks to the yoke 55 through the insulators 68. Accordingly, the magnetic flux cannot be efficiently used.
The permanent magnets 59, 60 have the magnet pieces 59a, 59b, 60a, 60b and the resin pieces T that magnetically separate the magnet pieces from each other. The DC motor 50 further includes the core plates 67 through which the magnetism from the corresponding magnet pieces permeates and the insulators 68 that magnetically separate the permanent magnets 59, 60 from the fixed yoke 55. Thus, the number of parts that constitute the DC motor 50 is increased, which complicates the assembly of the motor 50.
Accordingly, it is an objective of the present invention to provide a hybrid magnet type DC motor in which magnetic flux does not leak much and the structure is simple.
To achieve the above objective, the present invention provides a hybrid magnet type DC motor including a commutation device, an armature, a cylindrical stator and a fixed yoke. The armature has a rotation core and a plurality of rotation coils that are wound around the rotation core. Direct current is supplied to the rotation coils through the commutation device. The cylindrical stator is constituted as a hybrid magnet. The cylindrical stator has a circumferential direction, a radial direction, and an axial direction. The stator has a plurality of electromagnets and permanent magnets that are alternately arranged in the circumferential direction of the stator. Each electromagnet has a fixed core and a fixed coil that is wound around the fixed core. Each fixed core has a pole core that faces to the rotation core and has an approximately arched cross-sectional shape. When direct current is supplied to the fixed coils, the pole cores are alternately magnetized to be N- and S-poles in the circumferential direction of the stator. The fixed yoke through which magnetism permeates is magnetically separated from the permanent magnets and contacts the fixed cores. The permanent magnets are anisotropic magnets. Each permanent magnet includes a first curved surface and a second curved surface opposite to the first curved surface. The first curved surface is magnetized and the second curved surface is non-magnetized. The first curved surface of each permanent magnet contacts two pole cores that are arranged in both sides of each permanent magnet in the circumferential direction of the stator and have different polarities from each other. The first curved surface has an S-pole portion and an N-pole portion. The S-pole portion is provided in one side of the first curved surface in the circumferential direction and the N-pole portion is provided in the other side of the first curved surface in the circumferential direction. The S-pole portion contacts the pole core that is magnetized to be an S-pole and the N-pole portion contacts the pole core that is magnetized to be an N-pole.